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Like wind turbines, wave energy devices can be clustered in “wave farms” near the shorelines or moved off-shore. The main advantages of near-shore plants are that they are much cheaper to construct and there is less distance for electrical cables to be laid on the ocean floors. Their main disadvantage is that waves break up and lose much of their energy as they approach the coastlines. Shore-based stations are mostly considered for small-scale electricity generation. Offshore devices have the advantage of being more efficient, and they are not as unsightly to the public as the near-shore facilities. No matter which approach is used there are always some navigational hazards to shipping and other marine transportation.

Contents

Economical Concerns

Power output from a hydroelectric station increases with the flow rate of the water and its available head. For a given power output, less water is required for the higher head so the plant size would be smaller and the cost of construction and equipment would be lower. Unfortunately, taller waterfalls tend to be in mountainous regions and areas with lower population density. Therefore, transmission costs of electricity may be higher. Thus, before selecting the plant site, it is important to consider not only the total power but also the initial cost, operating cost, and cost of transmission. Typically the installed cost of hydro electrification projects is about $1,000-1,500 per kW for large, $2,500-3,000/kW for small (2.5-25 MW), and $10,000/kW for micro (below 500 kW) hydro projects. (1)

Environmental Concerns

Hydropower technologies have many of the same advantages of other renewable energy sources. They are clean, do not leave any waste, do not contribute to global warming, nor do they produce any of the air pollutants that result from the combustion of fossil fuels.( a ) The large reservoirs formed behind hydroelectric dams or tidal plants can provide a barrier against storm surges and benefit the public by providing beaches for swimming, fishing, and other recreational activities. Hydropower has an additional advantage over other renewable sources such as solar and wind in that it is a lot more reliable.

This does not mean that hydropower is without any environmental impact, however. Some of the concerns specific to hydroelectric and tidal projects are:

a. Interrupting the natural flow of a river – Change in river condition and adjacent lands may impact fish and aquatic population, threaten wildlife natural habitats, affect vegetation, and degrade shorelines.

b. Affecting water quality – Impounding water flow raises the surface water temperature which in turn affects the concentration of dissolved oxygen and other nutrients, and allows certain bacteria to grow in hydro rivers and reservoirs, which may potentially pose a health hazard.

c. Causing floods – Although dams can act as a flood control measure, there are also concerns for the flooding of lakes and rivers upstream of the plant. In addition, a dam failure in the event of an earthquake or other disaster could cause immediate flooding of the area below the dam, costing society countless lives and great economical loss.

d. Impeding the natural transport of sediments – Restricting the amount of water flow results in a reduction in sedimentation in the river downstream of the dam and an accumulation of silt in lakes behind the dam. As the storage volume becomes filled with silt, the generation capacity of the plant is reduced and the stored water may require periodic dredging and flushing of sediments at a considerable cost.

e. Displacing Population – Large hydropower projects will have a huge impact on the surrounding population. Many people have to be relocated which in turn may have considerable impacts on the local economy.

The major concerns raised against wave power are their vulnerability to violent storms, aesthetics, noise, and the additional costs if electricity is brought to land.

References

(1) Mayo, N., “Ocean Waves - Their Energy and Power,” The Physics Teacher, 35, pp. 352-356, Sep. 1997.

Additional Comments

(a) What differentiates hydroelectric and wind plants from thermal plants is that in hydroelectric and wind plants water or air flow directly through the turbine, whereas in thermal power plants, fossil or nuclear fuels heat water to steam before it flows through the steam turbine.

Further Reading

Bose, N. and Brooke, J., Wave Energy Conversion, Elsevier, 2003.

Ross, D., Energy from the Waves, Oxford University Press, 1995.

Cruz, J., Ocean Wave Energy: Current Status and Future Perspectives, Springer Series in Green Energy and Technology, Springer-Verlag, Berlin, 2008

International Journal of Wave Motion, Elsevier Science Publishing Company.

International Journal of Renewable Energy, Elsevier Science Publishing Company.

External Links

National Oceanic and Atmospheric Administration (NOAA) Coastal Services Center (http://www.csc.noaa.gov).

European Commission on Tidal Energy (http://europa.eu.int/comm/energy_transport/atlas/htmlu/tidal.html).

OTEC, U.S. DoE, Energy Efficiency and Renewable Energy (http://www.eere.energy.gov/RE/ocean.html).

Wave Energy Council: Survey of Energy Resources (http://www.worldenergy.org/wec-geis/publications/reports/ser/wave/wave.asp).